EP0545766A1 - Ferruginous coolant producing method for steel making in converters and so produced coolant - Google Patents

Abstract

Process for the preparation of a cooling agent containing iron for refining steel in a steelworks converter. The cooling agent is made of balls produced from rolling mill fatty sludge. The present invention also relates to a cooling agent containing iron obtained by this process.

Description

The present invention relates to a process for the preparation of a cooling agent containing iron for refining steel in a steelworks converter.

The present invention also relates to a cooling agent containing iron produced by this process.

In integrated steel plants, rolling operations and in particular hot rolling require the use of lubricating oil and cooling water.

The unburnt oil and the scale mix and are entrained by the cooling water to the sand filters placed in the water recovery circuit.

When these filters are too dirty, they are backwashed with water, producing fatty sludge from rolling mills in which iron-containing residues are polluted by the hydrocarbons from the oil.

This fatty sludge which is recovered at the rate of 1000 tonnes per month in certain steel mills, is stored in a lagoon and is never used.

In addition, this fatty sludge infiltrates the soil over time and pollutes the groundwater.

Given the drawbacks inherent in the storage of fatty sludge from rolling mills and the non-use of this iron-containing product, the Applicant has carried out numerous revalorization tests and has discovered quite unexpectedly that this sludge can be used in a steelworks converter as a cooling agent, after having underwent appropriate treatment.

• on ajoute aux boues grasses de laminoirs extraites, de la chaux, du minerai de fer, des scories et des fibrilles métalliques afin d'obtenir un mélange dont la composition pondérale est la suivante :
  • . boues grasses : 55 à 93%
  • . chaux : 5 à 25%
  • . fibrilles métalliques : 5 à 15%
  • . minerai de fer: 1 à 15%
  • . scories : 1 à 15%
• on laisse reposer ledit mélange sous abri en vue de l'extinction de la chaux,
• on homogénéise le mélange obtenu,
• on ajoute 4 à 10% de liant,
• et on compacte ledit mélange pour former les boulets.

The present invention thus relates to a process for the preparation of a cooling agent containing iron, characterized in that said agent is formed of balls produced from fatty sludge from rolling mills and in that:

• lime, iron ore, slag and metal fibrils are added to the fatty sludge from extracted rolling mills in order to obtain a mixture whose weight composition is as follows:
  • . fatty sludge: 55 to 93%
  • . lime: 5 to 25%
  • . metallic fibrils: 5 to 15%
  • . iron ore: 1 to 15%
  • . slag: 1 to 15%
• the said mixture is left to stand under shelter with a view to slaking the lime,
• the mixture obtained is homogenized,
• 4 to 10% of binder is added,
• and compacting said mixture to form the balls.

• les boulets ont une forme générale d'ellipsoïdes de longueur comprise entre 20 et 60mm et d'épaisseur comprise entre 10 et 25 mm,
• les fibrilles métalliques ont une longueur maximale d'environ 5mm et un diamètre moyen d'environ 0, 3mm,
• les fibrilles métalliques sont des copeaux issues d'opérations d'usinage telles que le meulage,
• les fibrilles métalliques contiennent du fer,
• la composition pondérale du mélange est de préférence la suivante :
  • . boues grasses : 76 à 80%
  • . chaux : 10 à 12%
  • . fibrilles métalliques : 7 à 12%
  • . minerai de fer : 1 à 6 %
  • . scories : 1 à 6 %

According to other characteristics of the invention:

• the balls have a general shape of ellipsoids of length between 20 and 60mm and thickness between 10 and 25 mm,
• the metallic fibrils have a maximum length of approximately 5mm and an average diameter of approximately 0.3mm,
• the metallic fibrils are chips resulting from machining operations such as grinding,
• metallic fibrils contain iron,
• the weight composition of the mixture is preferably the following:
  • . oily sludge: 76 to 80%
  • . lime: 10 to 12%
  • . metallic fibrils: 7 to 12%
  • . iron ore: 1 to 6%
  • . slag: 1 to 6%

• au moins 50% à 67% de fer
• de 8 à 18% de chaux
• moins de 0,2% de soufre
• moins de 7% de carbone
• moins de 10% de résiduels sous forme alcaline et minérale, le fer étant présent sous forme libre et sous forme d'oxydes.

The present invention also relates to a cooling agent containing iron produced by the process mentioned above, characterized in that it contains by weight:

• at least 50% to 67% iron
• 8 to 18% lime
• less than 0.2% sulfur
• less than 7% carbon
• less than 10% residual in alkaline and mineral form, the iron being present in free form and in the form of oxides.

The description which follows, given by way of nonlimiting example, will make it possible to better understand the invention and to highlight the advantages and characteristics of the invention.

In a steelworks converter, the steel is refined in order to produce a crude steel with characteristics which are not very dispersed around the target values, that is to say limit values for the contents of impurities such as phosphorus or sulfur for example, a minimum temperature compatible with shading and a temperature for casting in a continuous casting machine and, moreover, a carbon content.

When the liquid pig iron and the scrap are loaded into the converter, about 15,000m3 of oxygen is blown in for several minutes by means of a blowing lance for the production of steel.

At the start of the oxygen insufflation phase, the lime is placed in the oven, which will react with the oxygen and with the elements present in the cast iron such as for example silicon, phosphorus and manganese in order to form slag or else what is called the converter slag.

After the lime has been put in the oven, the coolant is put into place by gravity, which is traditionally a so-called blowing ore containing about 67% iron in the form of oxides and which contributes to the energy balance of the refining.

The process according to the invention consists in preparing a cooling agent containing iron formed from balls produced from fatty sludge from rolling mills.

This agent is intended to partially replace the traditional blowing ore and it is planned, for example, to replace 3 tonnes of ore with 4.5 tonnes of agent according to the invention in order to satisfy the energy balance and to obtain a composition and a determined steel temperature.

The free carbon in the form of a hydrocarbon must be present in the agent in proportions not exceeding 7%, in order to avoid the risk of conversion of the hydrogen atoms of the hydrocarbon chains coming from the fatty sludge of rolling mills into molecules gas.

Indeed, the presence of a gaseous volume of hydrogen in the converter and therefore in the collecting duct arranged above can cause explosions of considerable power.

The iron-containing cooling agent according to the present invention is produced from fatty sludge from rolling mills stored in a lagoon.

The first step in the manufacturing process consists in extracting this sludge and incorporating additives which will transform it and give it specific properties.

Thus, quicklime is added, for example, in order to dry the sludge and to oil it.

The role of lime is to bring the humidity down to around 4 to 5% maximum.

Since the chemical reaction is exothermic, the temperature being close to 80 ° C, a fraction of the hydrocarbons is thus eliminated by evaporation, the other fraction being fixed on the lime.

An excess of lime can cause the balls of the iron-containing agent to burst, thus strongly preventing the penetration of said product into the liquid bath of the converter, which has the effect of disturbing the production of the steel, leading to a higher temperature steel than expected.

To this end, no more than 25% lime should be added.

Below 5%, partial deoiling and the addition of lime becomes ineffective.

Also added 1 to 15% of iron ore, preferably 1 to 6%, in the form of a powder whose particle size spectrum is less than 5mm in its entirety as well as 1 to 15%, preferably 1 to 6% , slag from the converter and reprocessed.

Slag is fines smaller than 3.14mm.

The mixture thus formed contains 55 to 93%, preferably 76 to 80%, of fatty mud by weight.

The Applicant has moreover found that balls produced from fatty sludges from rolling mills, lime and possibly iron ore and slag do not have sufficient cohesion.

Therefore, when the balls are placed in the converter, they are in contact with intense heat, the temperature prevailing in the enclosure of the converter approaching 1500 ° C., and by a lack of cohesion disintegrate before entering the liquid iron bath, producing a considerable quantity of fines.

The fines are then sucked into the collection duct and are deposited on the walls of said duct, thus causing fouling of the latter.

These fine aspirates also represent a non-negligible part of the cooling agent which does not participate in the energy balance of the converter and which therefore has no thermal efficiency.

To this end, the Applicant has surprisingly discovered that the addition of 5 to 15% and preferably 5 to 12% of metal fibrils to the above-mentioned mixture gives the balls better cohesion and makes it possible to reduce by approximately 30% the proportion of fines in the balls thus delaying the disintegration of said balls when they are placed in the converter. The metallic fibrils have a maximum length of around 5mm and an average diameter of around 0.3mm.

Indeed, for dimensions greater than those previously mentioned, it is found that the balls no longer have the desired cohesion.

These fibrils are metal chips from machining operations such as for example grinding and can contain iron.

These iron-containing metal shavings are for example made of stainless steel, but they can also be made of steel of any other type such as, for example, mild steel.

The metal chosen is not limited to steel and can for example be aluminum or any other metal.

The mixture obtained is then left to stand under shelter for about a week. The purpose of this step is function of quenching the lime and also intervenes by increasing the mechanical resistance of the mixture over time.

This rest time is variable, depending on the contents used in the mixture, from a few days to three weeks.

When the mixture is rested, it is homogenized in a mixer.

The penultimate step relates to the addition of binder in proportions of between 4 to 6% and preferably equal to 5%.

As binder, cane molasses is chosen which acts on the mixture by creating mobile liquid bonds and then, after drying, solid bridges which bond the grains of said mixture to each other.

The binder thus contributes to improving the mechanical resistance of the cooling agent.

After drying, the mixture contains less than 2% water.

Binders such as ammonium lignosulfonate and calcium lignosulfonate can also be used.

The shaping of the iron-containing cooling agent according to the present invention constitutes the last stage of its manufacture and takes place in a compacting press under a pressure of 400 to 500 bars.

Balls are thus formed which have the shape of ellipsoids whose dimensions are such that the length is between 20 and 60mm and the thickness is between 10 and 25mm.

The form chosen for the coolant is the most suitable for its transport to the converter.

Indeed, when the coolant is conveyed to the converter using bands conveyors, these are often inclined so that a cooling agent developed in the form of spheres is not suitable.

It should also be noted that a cooling agent produced in the form of a briquette or parallelepiped is no more suitable for this routing, given the fact that it has sharp edges which withstand shock badly and that it crumbles quite easily during transport to the converter which is not the case of the very compact balls of the present invention.

The size of the balls, their density and their mechanical strength allow, when they are placed in the converter, to easily penetrate into the liquid bath, thus promoting the reaction with the liquid metal.

The mechanical resistance of the balls has also greatly increased with the addition of metallic fibrils.

Indeed, the Applicant has been able to note that the balls produced without metal fibrils exhibited a mechanical resistance to compression of the order of 25 Kgf while those produced with said metal fibrils exhibited a mechanical resistance to compression of the order of 85 Kgf.

• 52% de fer sous forme libre et oxydée
• 9,8% de chaux
• 0,08% de soufre
• 6,5% de carbone
• le reste étant constitué de moins de 10% de résiduels sous forme alcaline et minérale.

The iron-containing cooling agent according to the present invention has, for example, the following chemical composition:

• 52% iron in free and oxidized form
• 9.8% lime
• 0.08% sulfur
• 6.5% carbon
• the remainder being made up of less than 10% of residuals in alkaline and mineral form.

It should be noted that the sulfur content must be less than 0.2% due to the fact that steelmakers find it difficult to get rid of excess sulfur in the steel to the converter.

The present invention therefore makes it possible to recycle iron-containing residues present in the fatty sludge of rolling mills stored in the lagoon for many years, as well as those produced daily on rolling mill trains.

Removing this sludge from the lagoon also eliminates the risk of pollution of the groundwater.

In addition to these advantages, the invention makes it possible to carry out the refining under the best possible economic conditions by reducing the cost of charging the ore with the converter.

Tests have been carried out on balls without fibrils and with fibrils to quantify the impact of the addition of said fibrils on the proportion of fines of said balls.

• boues grasses 77,1%
• chaux 10,5%
• minerai de fer 4,2%
• scories 4,2%
• liant 4%

puis, on a élaboré des boulets noté B par adjonction de 10% de fibrilles au mélange précédent. Ces fibrilles sont des copeaux d'acier inoxydable de longueur maximale égale à 5mm et de diamètre moyen égal à 0,3mm, issus d'une opération de meulage.First of all, balls marked A were formed and formed from the following composition, according to the method described above, without the addition of fibrils:

• fatty sludge 77.1%
• lime 10.5%
• iron ore 4.2%
• slag 4.2%
• binding 4%

then, balls marked B were prepared by adding 10% of fibrils to the previous mixture. These fibrils are stainless steel shavings of maximum length equal to 5mm and of average diameter equal to 0.3mm, resulting from a grinding operation.

• boues grasses 70%
• chaux 9,2%
• fibrilles 9,2%
• minerai de fer 3,8%
• scories 3,8%
• liant 4%

The new mixture therefore has the following composition:

• oily sludge 70%
• lime 9.2%
• fibrils 9.2%
• iron ore 3.8%
• slag 3.8%
• binding 4%

In each of the two aforementioned cases A and B, 150 kg of balls 60 mm long and 25 mm thick were prepared.

For each case A and B, a test called MICUM test is carried out on 15 kg of cooling agent.

The purpose of such a test is to measure the generation of fines during the passage of the balls over a MICUM drum.

This drum simulates the degradation undergone by the material during the various handling operations.

• déposer 15kg d'agent refroidissant élaboré sous la forme de boulets sur une roue munie d'une cornière périphérique de 50mm de largeur et tournant à une vitesse de 200 tours par minute pendant cinq minutes. Au cours de la rotation de la roue une partie des boulets se désagrège et est récupérée dans la cornière,
• recueillir les boulets restants et la partie désagrégée récupérée dans la cornière et à les tamiser de manière classique sur des tamis à mailles circulaires de diamètres successifs 60, 40, 20, 10, 5 et 3,14mm.

The MICUM test is carried out according to an ISO standard and consists successively for each case A and B of:

• place 15 kg of cooling agent produced in the form of balls on a wheel fitted with a peripheral angle 50mm wide and rotating at a speed of 200 revolutions per minute for five minutes. During the rotation of the wheel, part of the balls breaks up and is recovered in the angle iron,
• collect the remaining balls and the disaggregated part recovered in the angle iron and to sieve them in a conventional manner on sieves with circular meshes of successive diameters 60, 40, 20, 10, 5 and 3.14 mm.

The purpose of this test is to obtain the particle size spectrum of the balls and therefore to evaluate the quantity of fines present in said balls.

Thus after the first test, we obtain the results recorded in Table 1 below:

The 135 kg of cooling agent which has not undergone this test are then in both cases A and B exposed in a sintering oven for a period of 5 minutes at a temperature between 950 and 1020 ° C.

We then proceed, 24 hours after for each case, to a MICUM test on 15 kg of balls which have undergone the previous heat treatment.

The results of this second test are expressed in the following table 2:

These results therefore make it possible to note that the addition of stainless steel fibrils in the balls of coolant reduces by about a third the proportion of fines, that is to say dust of dimensions less than 3.14 mm, and improves the cohesion of the balls.

The addition of metal fibrils of particular dimensions therefore makes it possible, when the balls are placed in the converter, to increase their cohesion due to their better thermal conductivity and thus to delay the phenomenon of disintegration which allows more of the balls reach the liquid metal bath and therefore participate in the heat balance by playing the role of cooling agent.

Claims (9)

Process for the preparation of an iron-containing cooling agent for refining steel in a steelworks converter, characterized in that said agent is formed from balls produced from fatty sludge from rolling mills, and in that: - lime, iron ore, slag and metallic fibrils are added to the fatty sludge from extracted rolling mills in order to obtain a mixture whose weight composition is as follows: . fatty sludge: 55 to 93% . lime: 5 to 25% . Metallic fibers: 5 to 15% . iron ore: 1 to 15% . slag: 1 to 15% - the said mixture is allowed to stand under shelter with a view to the extinction of the lime, - the mixture obtained is homogenized, - 4 to 10% of binder is added, - And compacting said mixture to form the balls. Method according to claim 1, characterized in that the balls have a general shape of ellipsoids of length between 20 and 60 mm and of thickness between 10 and 25 mm. Method according to claim 1, characterized in that the metal fibrils have a maximum length of approximately 5mm and an average diameter of approximately 0.3mm. Method according to any one of claims 1 and 3, characterized in that the metal fibrils are chips from machining operations such as grinding. Method according to any one of claims 1, 3 and 4, characterized in that the metallic fibrils contain iron. Method according to claim 1, characterized in that the weight composition of the mixture is preferably the following: . oily sludge: 76 to 80% . lime: 10 to 12% . metallic fibrils: 7 to 12% . iron ore: 1 to 6% . slag: 1 to 6% Method according to claim 1, characterized in that 4 to 6% of binder is preferably added. Process according to claim 1, characterized in that the binder is chosen from cane molasses, ammonium lignosulfonate and calcium lignosulfonate. Cooling agent containing iron produced by the process according to any one of Claims 1 to 8, characterized in that it contains by weight: - from 50 to 67% iron - 8 to 18% lime - less than 0.2% sulfur - less than 7% carbon - less than 10% of residuals in alkaline and mineral form, the iron being present in free form and in the form of oxides.